1. Field of the Invention
The present invention relates generally to a ventilator of the heat exchange type which comprises centrifugal fans provided in an air passageway for discharging indoor air outdoors and for introducing outdoor air into a room to be ventilated, the centrifugal fans being alternately driven, and more particularly to such an apparatus wherein either of the centrifugal fans is formed of a heat-accumulative material and wherein heat exchange is performed by accumulating heat in the centrifugal fan formed of the heat-accumulative material during indoor air exhaust operation to thereby dissipate the heat to outdoor air during outdoor air suction operation.
2. Description of the Prior Art
Prior art ventilators of the heat exchange type generally comprises, as disclosed in Japanese Utility Model Provisional Publication No. 38668 of 1984, a crossflow heat exchanger and a pair of fan means for introducing outdoor air into the room through the heat exchanger and for discharging indoor air outdoors. As well known in the art, the cross-flow heat exchanger is so constructed that two crossed air flow paths are alternately formed by stacking a number of heat transfer discs with corrugated discs sandwiched therebetween. The heat exchange is performed by introducing the indoor air and the outdoor air into the crossed air flow paths by the fan means.
In the above-described cross-flow heat exchanger, since heat is transferred in accordance with the difference between the temperatures of indoor air and outdoor air flowing along respective sides of the heat transfer plates, heat transfer efficienty is inevitably decreased owing to heat resistance of the heat transfer plates. Furthermore, the corrugated discs occupying most of the inside surface of each air flow path do not serve for the heat exchange and it is the heat transfer plates occupying only part of the inside surface of each air flow path that actually serve for the heat exchange. Consequently, sufficient heat exchange cannot be obtained in the prior art ventilators of the heat exchange type. To provide sufficient heat exchange capacity, the heat exchanger needs to be rendered large-sized, which causes the ventilator to become large-sized.
To overcome the above-described disadvantages, Japanese Patent Provisional Publication No. 107848 of 1980, for example, discloses an improved construction that each flat disc fan comprises a number of flat discs formed of the heat-accumulative material and that the flat discs are stacked in a spaced apart relation. Outdoor air suction and indoor air exhaust operations are alternately performed by alternately inducing transverse air flows in the opposite directions when the flat disc fans are rotated in the forward and reverse directions alternately. According to this construction, since the suction air and exhaust air alternately flow through an identical air passageway, the heat exchange is performed by accumulating heat in the flat discs and by dissipating the heat therefrom. Consequently, the heat exchange efficiency is improved as compared with the cross-flow heat exchanger.
However, the static pressure of air is inherently low in the case of the flat disc fan. The need thus remains to improve the ventilator of the heat exchange type in its blowing capacity. Additionally, each air path formed in the flat disc fans has a flat surface configuration and the transverse air flow is biased in the flat disc fans. As a result, sufficient heat exchange area cannot be obtained. The need also remains to improve the ventilator of the heat exchange type on the point of heat exchange efficiency.